1) Field of the Invention
This invention relates to sterilization, and more particularly to a process and apparatus for effecting plasma sterilization using low molecular weight aliphatic alcohols, preferably methanol.
2) Description of the Prior Art
There is a growing concern about the spread of infections during routine healthcare treatments due to public awareness of transmissible diseases including hepatitis and AIDS, also echoed by the CDC (Center for Disease Control) and the FDA (Food and Drug Administration) currently focused on nosocomial infection. A plethora of sterilization techniques are and have been practiced for years using heat, sterilization agents and the like, as well as including the use of plasma sterilization techniques. For instance in U.S. Pat. No. 3,383,163, there is disclosed the use of an argon RF plasma to sterilize the interior walls of glass bottles. A chemically reactive halogen gas RF plasma is disclosed in U.S. Pat. No. 3,701,628 to achieve sterilization at lower temperatures and while suitable for glass and plastic bottles, such method is corrosive to metals.
In U.S. Pat. No. 4,207,286, there is disclosed a method for passing an aldehyde feed gas RF plasma over objects to achieve surface sterilization. In U.S. Pat. No. 4,348,357, there is disclosed the use of pressure/power cycles to convectively force the (oxygen) RF plasma species into holes, apertures and cavitites as well as to sterilize objects of irregular shape. In U.S. Pat. No. 4,599,216, there is disclosed an apparatus for increasing the uniformity of microwave exposure by rotating dental items through the microwave field. A microwave adsorber is necessary to reduce the likelihood of metal objects arcing back to the magnetron, however, long exposures obtained erratic results--insufficient to justify claims of sterility.
In U.S. Pat. No. 4,643,876, there is disclosed the use of hydrogen peroxide (liquid) in the pre-treatment cycle and (vapor) as a precursor for active species made in an RF plasma. In U.S. Pat. No. 4,756,882 there is described the conversion of residual hydrogen peroxide into non-toxic decomposition products. In U.S. Pat. No. 4,801,427 there is disclosed the use of hydrogen, oxygen, nitrogen, halogens, organohalogens, inorganic halogens, inorganic oxyhalogenated compounds, inert gases and mixtures to produce RF plasmas to sterilize medical instruments. In U.S. Pat. No. 4,804,431, there is described the modification of a conventional microwave oven to produce oxygen or argon plasmas for etching and cleaning.
Traditional sterilization methods include: ethylene oxide gas which leaves toxic residues; dry heat which may corrode metal; steam autoclaving dulling blades and points; chemical vapor (e.g. formaldehyde and gluteraldehyde); gamma, x-ray and electron beam/curtain radiation which is only suitable for batch or production line processing, etc. While all such techniques have achieved satisfactory levels of sterilization for particular uses of the thus sterilized item, such techniques suffer from universality to the materials of construction of items to be sterilized as well as requirements to store dangerous chemical sterilants with concomitant handling difficulties. Additionally, such techniques are ineffective in situations requiring rapid sterilization, e.g. in a surgical procedure when a critical instrument is unsterile, dropped or otherwise contaminated.